To get this trophy, you must complete Mystery Foe without using Blink, Dark Vision, Possession, or Bend Time.

It is helpful to knock out the 3 patrolling guards in the first area before proceeding. Open the doors ahead of the starting point, sleep dart the first guard, and carry him back into the starting room. Repeat this for 2 more guards when they pass by the room, and that takes care of the patrol. There is a fourth guard standing stationary just beyond the doors down the hallway, to the right of the starting point. If the clue locations take you this direction, sneak up behind him, choke him out, and hide the body.

With these 4 out of the way, the level is relatively clear. Occasionally, someone may walk out of an open doorway, so proceed with a little caution. If at any point you are detected, use sleep darts to subdue the person.

Now sneak around and pick up the 4 clues to reveal your target. Once the target is dispatched, the trophy will unlock.